<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div>
        <button id="b1">第1个按钮</button>
        <button>第2个按钮</button>
        <button>第3个按钮</button>
        <button>第4个按钮</button>
        <button>第5个按钮</button>
    </div>

    <script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.5.1/jquery.slim.min.js"></script>
    <script>
        $('#b1')
        .css({color: 'white'})
        .css({background: 'blue'})
    </script>
</body>
</html>